Field of the Invention
This invention relates to a signal processing apparatus which converts a signal such as a video signal to another signal having an arbitrary amplitude-frequency characteristic with flat group delay-frequency characteristic, and therefore is usable in a video signal transmission system such as a video tape recorder and a satelite broadcasting system.
In a conventional video tape recorder the video signal is frequency modulated to be recorded on a video tape. In the frequency modulating system in which the white noise is contained in the FM transmission path, the power spectrum of the noise contained in the demodulated signal increases in proportion to the frequency. In order to reduce the noise, the intermediate and high frequency components of the video signal is emphasized (emphasis), or widened in frequency deviation range, before being frequency modulated, and after frequency demodulated de-emphasized (de-emphasis). On the other hand, the frequency range of the FM transmission path is limited by the frequency range (performance) of the electromagnetic conversion system such as the magnetic tape and the magnetic head. Due to this frequency range limitation, the amount of emphasis (emphasis factor) is limited or the signal must be clipped after emphasized. The small amount of emphasis causes a poor S/N (signal to noise ratio), and the signal clipping causes a signal distortion. This problem occurs in any FM transmission systems such as video tape recorders and satelite broadcasting systems.
Further, when a video signal is processed to obtain an arbitrary amplitude-frequency characteristic, a group delay distortion is caused so that the waveform of the processed video signal is distorted. Therefore, a practical signal processing apparatus having a flat group delay-frequency characteristic has been desired.